Polyhalomethane compounds are used as photopolymerization initiators and in applications such as silver halide photographic materials. Conventionally known polyhalomethane compounds are disclosed in, e.g., JP-B-54-165 (the term "JP-B" as used herein means an "examined Japanese patent publication"), U.S. Pat. Nos. 3,874,946 and 4,756,999, EP-A-605,981, and EP-A-631,176. Examples of these known polyhalomethane compounds are shown below. ##STR2##
(disclosed in JP-B-54-165) ##STR3##
(disclosed in JP-B-54-165) ##STR4##
(disclosed in EP 605,981 A1) ##STR5##
(disclosed in EP 631,176 A1)
On the other hand, photothermographic materials in which a photographic image is formed through heat development are disclosed, e.g., in U.S. Pat. Nos. 3,152,904 and 3,457,075 and in D. Morgan and B. Shely "Thermally Processed Silver Systems" (Imaging Processes and Materials, Neblette 8th ed., edited by Sturge, V. Walworth and A. Shepp, p. 2, 1969).
Such photothermographic materials contain a reducible silver salt (e.g., an organosilver salt), a catalytically effective amount of a photocatalyst (e.g., a silver halide), and a reducing agent, which all are usually dispersed in an (organic) binder matrix. The photothermographic materials are stable at ordinary temperature. Upon heating to a high temperature (e.g., 80.degree. C. or higher) after exposure, the photosensitive materials undergo an oxidation-reduction reaction between the reducible silver source (which functions as an oxidizing agent) and the reducing agent to yield silver. This oxidation-reduction reaction is accelerated by the catalytic action of the latent image formed by exposure. The silver yielded by the reaction of the organosilver salt in the exposed areas provides a black image, which makes a contrast with the unexposed areas. Thus, an image is formed. These sensitive materials optionally contain a tone regulator for regulating the color tone of the silver image. Such image-forming systems are apt to suffer fogging.
Mercury ions are known to be the most effective antifoggant in the prior art fogging-preventive techniques. Use of a mercury compound as-an antifoggant in a photosensitive material is disclosed in, e.g., U.S. Pat. No. 3,589,903. However, since use of mercury compounds is undesirable from the standpoint of environmental protection, polyhalomethane compounds such as those specified above have been developed so far as mercury-free antifoggants.
Those prior art mercury-free compounds specified above, however, have problems in that they are less effective in fogging prevention or impair the color tone of silver, and that a high antifogging effect is obtainable with a sacrifice of sensitivity. The prior art compounds should be improved in these points. Further, photosensitive materials containing such a prior art compound have a problem in that when they are stored in a stacked state under high-temperature high-humidity forced aging conditions and then subjected to exposure and development, enhanced fogging occurs in the unexposed areas. There has hence been a desire for an antifoggant free from these problems.